The present invention relates generally to multicylinder internal combustion engines of a variable displacement type in which a number of cylinders is deactivated in response to sensed engine load, and specificially it relates to an electronic fuel injection of the variable displacement type in which the deactivated cylinders are switched from one group to another when the engine is at maximum or minimum load.
Variable displacement internal combustion engines are known in the art to improve fuel economy by selectively shutting off fuel supply to several cylinders of the engine when reduced power output can operate the vehicle adequately. However, if deactivation takes place for an extended period of time, the deactivated cylinders will be cooled and thus there is hesitation in firing when the cylinders are reactivated by power demand. This problem is particularly serious if deactivation is incorporated in an electronic fuel injection since the deactivation can be effected simply by electrically cutting off the supply of injection pulses without providing additional components that permit the intake valves of the cylinders to close during deactivation. Therefore, air flow is sucked into the deactivated cylinders in each cylinder cycle as well as into the activated cylinders so that the deactivated cylinder is severely cooled as compared to the activated cylinders.
This hesitation problem can be alleviated by allowing the deactivation process to take place in a specified group of cylinders for a prefixed period of time and then switching the deactivation to occur in another group of cylinders for another prefixed period of time and repeating this process at intervals. However, the switching action occurs at predetermined intervals regardless of the varying engine loads, a mechanical shock can occur if switching takes place when the engine is at nearly full load.